1. Field of the Invention
The present invention relates to a method and an apparatus for controlling a reduction ratio of a continuously variable transmission of an automotive vehicle.
2. Description of the Prior Art
In a known continuously variable transmission disclosed in Japanese Patent Application provisional publication No. 56-46153 which appears to correspond to British Patent Application provisional publication GB No. 2,058,256A, the revolution speed of a drive pulley and the engine throttle opening degree (or the engine manifold vacuum) are detected to determine an actual engine operating condition, then the actual engine operating condition is compared with a predetermined ideal engine operating condition determined in accordance with a predetermined shift pattern to provide a deviation therebetween, and then the reduction ratio is controlled to decrease the deviation therebetween.
However, since, in the known continuously variable transmission, the reduction ratio is controlled along the same shift pattern as used in the ordinary operating condition even when the engine coolant temperature is low, the automotive vehicle can not operate smoothly because of a power shortage, and unpleasant engine vibration and engine stalling place during irregular engine operation when the engine coolant temperature is low.